Method and apparatus for operating a diesel engine under stoichiometric or slightly fuel-rich conditions

Abstract

A method and apparatus for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as is often necessary to maintain effective operation of certain post-combustion emission reduction devices, such as Lean NOx Traps, includes a readily vaporizable fuel injection nozzle disposed in the intake manifold system in communication with a combustion chamber of the diesel engine. The readily vaporizable fuel mixes with the intake air and produces a mixture of pre-mixed air and fuel when introduced into the combustion chamber. A diesel fuel, which is directly injected into the combustion chamber through a conventional diesel fuel injection nozzle. Combustion of the pre-mixed air and readily vaporizable fuel, with controlled injected of the diesel fuel, reduces the particulate matter (soot) emissions when operating the engine under the necessary stoichiometric or slightly fuel-rich conditions.

What is claimed is:  
     
       1. A method for operating a diesel engine under stoichiometric or slightly fuel-rich conditions includes: 
       providing a source of diesel fuel;  
       providing a source of a second fuel that is readily vaporizable in an air intake section of the diesel engine;  
       controllably introducing said readily vaporizable second fuel into said intake manifold system when said engine is operating under one of a stoichiometric and a fuel-rich operating condition, thereby providing a pre-mixed air/fuel mixture comprising air and said readily vaporizable second fuel;  
       introducing said pre-mixed fuel into a combustion chamber of said engine;  
       injecting said diesel fuel through an injection nozzle disposed in the combustion chamber of the diesel engine; and  
       combusting said diesel fuel and said readily vaporizable second pre-mixed air/fuel mixture in said combustion chamber.  
     
     
       2. The method, for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 1 , wherein the torque output of said diesel engine is controlled by modulation of a restriction in the air intake system of said engine. 
     
     
       3. The method, for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 1 , wherein the torque output of said diesel engine is controlled by modulation of a restriction in an exhaust system of said engine. 
     
     
       4. The method, for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 1 , wherein the torque output of said diesel engine is modulated by variable actuation of at least one of an intake valve and an exhaust valve in communication with said combustion chamber. 
     
     
       5. The method, for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 1 , wherein said second readily vaporizable fuel is selected from the group of fuels consisting of a volatile fraction of diesel fuel, gasoline, ethanol, methanol, natural gas, and liquified petroleum gas. 
     
     
       6. The method, for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 5 , wherein said second readily vaporizable fuel is generated by separation of the most volatile fraction of diesel fuel by partial distillation. 
     
     
       7. The method, for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 6 , wherein said diesel engine is mounted on a vehicle and said partial distillation is performed on-board said vehicle. 
     
     
       8. The method, for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 7 , wherein said distillation is performed by an evaporator and a condenser mounted on said vehicle. 
     
     
       9. The method, for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 8 , wherein said evaporator is maintained at a temperature of from about 180° C. to about 220° C. 
     
     
       10. The method, for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 7 , wherein said diesel engine includes an exhaust gas recirculation system having an exhaust gas cooler disposed in said exhaust gas recirculation system, and said method includes heating said evaporator by said exhaust gas recirculation cooler. 
     
     
       11. An apparatus for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, said diesel engine having at least one combustion chamber, and an intake air system and an exhaust gas system in communication with said combustion chamber, wherein said apparatus includes: 
       a diesel fuel injection nozzle disposed in said combustion chamber of said engine and in communication with a source of diesel fuel;  
       a second injection nozzle disposed in said air intake system in communication with said combustion chamber and in communication with a second fuel that is readily vaporizable in said intake system;  
       a sensor for sensing the air/fuel ratio of the air/fuel mixture introduced into said combustion chamber;  
       a controller in communication with said sensor and with said diesel fuel and with said second readily vaporizable fuel, said controller controlling the injection of said diesel fuel and said second readily vaporizable fuel through said diesel fuel injection nozzle and said second injection nozzle disposed in the intake system, and injecting the second readily vaporizable fuel through the second injection nozzle disposed in the intake manifold system in response to said controller determining that the air/fuel mixture in said combustion is one of a stoichiometric and a fuel-rich mixture.  
     
     
       12. The apparatus for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 11 , wherein said apparatus includes a modulatable airflow restrictor disposed in the intake system of said engine, the torque output of said engine being controlled in response to modulating said airflow restrictor disposed in the air intake system. 
     
     
       13. The apparatus for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 11 , wherein said apparatus includes a modulatable exhaust gas restrictor disposed in the exhaust gas system of said engine, the torque output of said engine being controlled in response to modulating said restrictor disposed in said exhaust gas system. 
     
     
       14. The apparatus for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 11 , wherein said apparatus includes at least one of a variable intake valve and a variable output valve, in communication with said combustion chamber, the torque output of said engine being controlled in response to modulating at least one of said variable intake valve and said variable exhaust valve. 
     
     
       15. The apparatus for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 11 , wherein said second readily vaporizable fuel is selected from the group of fuels consisting of a volatile fraction of diesel fuel, gasoline, ethanol, methanol, natural gas, and liquified petroleum gas. 
     
     
       16. The apparatus for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 11 , wherein said volatile fraction of diesel fuel is a product of partial distillation of diesel fuel. 
     
     
       17. The apparatus for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 16 , wherein said diesel engine is mounted on a vehicle and said apparatus includes a diesel fuel distillation unit mounted on said vehicle. 
     
     
       18. The apparatus for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 17 , wherein said distillation unit includes an evaporator and a condenser mounted on said vehicle. 
     
     
       19. The apparatus for operating a diesel engine under stoichiometric or slightly fuel-rich conditions, as set forth in  claim 18 , wherein said engine includes a controllable exhaust gas recirculation system having an exhaust gas cooler disposed therein and said evaporator is heated by said exhaust gas recirculation cooler.